Electric circuit breaker



Sept. 24, 1963 a. G. ABEL, JR., ETAL 3,105,172

ELECTRIC CIRCUIT BREAKER Filed Nov. 15. 1961 2 Sheets-Sheet 1 MSl/L/lT/O/V I I I TR/F C/RCU/T F01? BREAKERS H 8. 8

TR/P C/RCU/T FOR BREAKERS A5, a a

lNVENTORS. @EORGE 6. ABEL, JR, JOHN H. SPENCER,

B) I flTTOR/VEY.

Sep 1963' G. G. ABEL, JR., 'ETAL ELECTRIC CIRCUIT BREAKER Filed Nov. 13. 1961 2 Sheets-Sheet 2 /NVENTOR$ GEORGE 6. AB. ,JR.,

JOHN H. SPENCER,

ATTORNEY.

United States Patent 3,105,172 ELECTRIC CIRCUIT BREAKER George G. Abel, Jr., and John H. Spencer, Media, Pa., assignors to General Electric Company, a corporation of New York Filed Nov. 13, 1951, Ser. No. 151,610 '7 Claims. (Cl. 317--) This invention relates to an electric circuit breaker of the type that comprises a housing at high potential in which circuit interruption is effected. More particularly, the invention relates to a circuit breaker of this type in which the housing of the circuit interrupter is mounted on the insulating enclosure of a high voltage current transformer.

A circuit breaker of this general type is shown and claimed in US. Patent 2,931,95l-Wilson, assigned to the assignee of the present invention. A particular advantage of the Wilson circuit breaker is that the current transformer equipment forming a part of the breaker is capable of accurately distinguishing between a wide variety of different types of circuit faults, even though the usual secondary windings of the transformer equipment are located in a single housing rather than at opposite terminals of the breaker. A disadvantage of the circuit breaker of the Wilson patent is that its overall height is too great to permit it to be shipped under ordinary conditions as a completely assembled unit.

An object of the present invention is to reduce the height of this general type of circuit breaker without materially impairing the ability of its current transformer equipment to accurately distinguish between a wide variety of different fault condiitons.

In carrying out our invention in one form, we provide a circuit breaker assembly that comprises a metallic housing at high potential and two sets of separable contacts disposed within the housing. Circuit interruption is effected within the housing by suitable means provided for separating the contacts of both sets. The assembly further includes an enclosure comprising a hollow insulating column and a tank disposed adjacent one end of the insulating column. The interrupter housing is supported on the other end of the column and the column serves to insulate the housing from ground. A current transformer primary winding is located electrically between the two sets of contacts, and insulation is provided for forcing current flowing between the two sets of contacts to follow a path through this primary winding. The primary winding comprises a pair of series-connected arms forming a loop. One of the arms extends from one set of contacts through the insulating column into the tank, and the other of the arms extends from the tank back through the insulating column to the other set of contacts. A first current transformer secondary winding is located in the tank and is inductively coupled to the primary conductor. A second current transformer winding is disposed with its magnetic circuit located externally to the enclosure and about both arms of the primary winding so that this sec- 0nd secondary winding is normally deenergized. Substantially all faults occurring within the enclosure are forced to follow a path to ground so located that the fault produces a net flow of current through the region disposed internally of the magnetic circuit of the second current transformer secondary winding. Substantially all faults external to the circuit breaker in the region of the insulating column are forced to consistently follow a breakdown path to ground which has a predetermined electrical location relative to the magnetic circuit of said second secondary winding.

For a better understanding of our invention, reference 3,l@5,l72 Patented. Sept. 24., 1963 may be had to the following specification taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a side elevational view partly in section and partly schematic showing a circuit breaker assembly embodying one form of our invention.

FIG. 2 is an enlarged sectional view of a portion of the circuit breaker of FIG. 1 showing more of the details of the circuit breaker.

FIG. 3 is a sectional view along the line 3-3 of FIG. 2.

FIG. 4 illustrates current transformer equipment included in a modified form of our invention.

Referring now to FIG. 1, there is shown a circuit breaker assembly A comprising a circuit interrupter 20 supported atop an enclosure 22. In the illustrated embodiment of the invention, the circuit interrupter 20 is of the gas-blast type and comprises a metallic tank 23 that is normally filled with pressurized gas. Disposed within the tank 23 are two sets 24 and 25 of separable interrupting contacts electrically connected together in series. The set 24 of contacts comprises 'a stationary contact 27 and a movable contact '28, and the set 25 of contacts comprises a stationary contact 29 and a movable contact 30. The movable contacts 25 and 30 are simultaneously operated by means of a pneumatically-controlled mechanism schematically shown at 32. This mechanism 32 and the contacts 24 and '25 can be of any suitable form but are preferably of the type shown and claimed in US. Patent 2,783,338-Beatty, assigned to the assignee of the present invention.

For supporting the stationary contacts 27 and 29 of the two sets of contacts, a pair of high voltage terminal bushings projecting horizontally through opposite ends of the metallic housing 23 are provided. These bushings respectively comprise rigid conductors schematically shown at 34 and 35 connected to the stationary contacts of the respective sets of contacts. The bushings further comprise porcelain cylinders 36 and 37, which respectively enclose the outer ends of the conductors 34 and 35 and also serve to support the conductors. These porcelain cylinders are in turn suitably supported upon the metallic housing 23. The fact that these bushings are disposed generally horizontally contributes to reduced overall height for the circuit breaker.

The enclosure 22 that supports the circuit interrupter 20 comprises a tubular porcelain column 40' provided with suitable fastening means 41 :at its top for rigidly securing the housing 23 to the top of the porcelain column 40. At the lower end of the porcelain column 40, a metallic tank 42 is provided. The upper portion of this tank 42 comprises a tubular throat 43, which is suitably fixed to an annular plate 45 that, in turn, is bonded to the porcelain column 40. Together the porcelain column 40 and the tank 42 form an enclosure 22 that is rendered gas-tight by suitable seals and gaskets provided at all of its joints. The space within the enclosure 22 is preferably isolated from the pressurized gas within the housing 23 of the interrupter.

One of the functions of the enclosure 22 is to support the circuit interrupter 20 on a base 46. To this end, a pair of L-shaped legs 47 are suitably secured to the tank 42 near its bottom and are, in turn, bolted or otherwise secured to the base 46. The tank 42 thus supports the column 40 which, in turn, supports the interrupter 20. To impart added rigidity to the tank walls in order to aid them in their supporting function, suitable reinforcing braces 48 are welded to the opposite walls. The tank 42 is solidly connected to ground by a connection 44 provided at a suitable location below the throat 43 of the tank. The porcelain column 40 provides for electrical isolation between the high voltage parts of the breaker and the grounded tank 42.

A second function of the enclosure 22 is to serve as 25, and 35 to the opposite terminal 59.

terminals of the current transformer.

a housing for the current transformer windings of the circuit breaker assembly. To this end, the enclosure 22 is filled with an insulating fluid, preferably a high dielectric strength gas suchyas sulfur hexafluoride, in which the various components of the current transformer are disposed. The primary conductor of the current, transformer is of a loop-shaped form and comprises .a pair of coaxially-disposed conductors, or arms, 50 and 51 extending through the porcelain column 40 into the tank 42 where their lower ends are electrically joined by a "generally toroidal shaped conducting element 52. More specifically; the conductive arm 50 comprises a rigid stud extending through the insulating column 40 into the tank 42, and the conductive arm 51 comprises a rigid tube surrounding the otherconductive arm 50 and locally insulated therefrom by means including an insulating spacer 4-9. The toroidal shaped conductor 42 is provided with a gap 52a to render i-t non-continuous and has its ends on opposite sides of the gap locally inmovable contacts v28 and the tubular contact 51, whereas conductor 55 extends between the movable contact 30 and the stud 50 of the. current transformer primary. Thus, the circuit through the circuit breaker assembly extends from one terminal 58 of the circuit breaker through the conductive parts 34, 24, 54, 51, 52, 50, 55, In this circuit the current transformer primary winding may be thought of as being located, electrically between the two sets 24 and 25 of contacts.

By locating the current transformer primary winding electrically'between the two sets of contacts 24 and 25 instead of at oneelectrical side of both setsvof contacts, as in the aforementioned Wilsonpateng'we can eliminate the need for the auxiliary insulating column provided in the Wilson circuit breaker between the tank 23 and the This enables us to'recluce the overall height of the circuit breaker by an amount generally equal to the height of the auxiliary insulating column of the Wilson patent. Another advantage of locating the current transformer primary electrically between the contacts 24 and 25 is that we can eliminate the rather expensive external connection provided in the Wilson circuit breaker between one terminal of the current transformer primary and the terminal of the circuit interrupter at the outer end of the bushing corresponding to the disclosed bushing 36, 34. 7

Referring now in greater detail to the current transformer assembly, the secondary windings of this assembly are shown at on and 61 disposed within the tank 42. Each of these windings is wound about its own annular magnetic core 63 encompassing the primary conductor 52. The turns of each of these windings are insulated from each other and from the core in :a conventional manner. Preferably these windings are enclosed by suitable grounded metallic housing 64 of a smooth configuration which serves to shield elcctrostatically the enclosed windings by preventing concentrations of electric housing 64 to provide the required levelofdielectric strength. The secondary windings 6i) and 61 are physically supported on the tank 42 by means of a suitable base plate 66 secured to the bottom of the tank. The leads from the windings 6i and 61 are brought out of the tank 42 through suitable sealed and insulated openings (not shown) provided in the bottom of the tank 42.

The above-described advantages of locating the current transformer between the two sets of contacts 214 and 25 have been obtained without materially impairing the ability of the current transformer equipment to distinguish between a wide variety of different fault conditions. To illustrate this point, the circuit breaker is shown connected in a typical po-wersystem with its current transformer secondaries 6t) and 61 connected in a conventional differential relaying system. In the power system of FIG. 1, the circuit breaker A serves as a bus-tie breaker interconnecting a pair of bus sections 11 :and 12. In the usual electric power system, a plurality of electric circuits, which may be either feeder or distribution circuits for respectively "supplying electrical energy to or from the bus, are connected to. each of the bus sections, but for simplicity, We have shown only a single circuit 13 connected to bus section 11 and a single circuit 14 connected to bus section 12. Circuit 13 is interconnected to'bus section 11 through a remote circuit breaker B, and circuit '14 is interconnected to the bus section 12 through a remote circuit breaker C. For the purposes of this description, these remote circuit breakers may be of a conventional construction and, hence are shown in schematic form only. It is desirable to isolate, or deenergize, only the faulty portion of the electrical power system upon the occurrence of a fault condition in order to permit uninterrupted service to be maintained. over the remainder of the system. To this end, if a rfault'should occur in an external portion of the circuitextending between the breakers, only the breakers at the terminals of the faulted external circuit portion should open. For

example, should a fault occur at F, it wouldbe necessary to open only breakers A and B, whereas breaker C should desirably remain 'operatively connected to its bus section. Thus, circuit 14, if a feeder circuit, could continue to supply power through bus section 12 to any other circuit (not shown) suitalbly connected to bus section 12. Such other circuit would ordinarily be connected to the 'bus section :12 through -a circuit breaker (not shown.) controlled by a suitable current transformer winding conat one side of the breaker and those external nected into the hereinafter-described protective circuit 82 in a conventional manner, such as is disclosed in US. Patent No. 2,804,576, Coggesh-all et 'al., assigned 'to the present invention. In a corresponding manner, if a fault should occur at G instead of F, it would be necessary to open only breakers A and C, whereas breaker B should remain operatively connected to its bus section 11 Whereby to permit this bus section to remain energized.

Since the faults F and G are external to the breaker, it will be apparent that there is little or no likelihood of their impairing the interrupting ability of the breaker. However, should a fault occur internally of the circuit breaker'A, there is a likelihood that the interrupting ability of the breaker A would be impaired, and possibly to such an extent that it would be unable to interrupt the current flowing into the fault. Assuming that the interrupting ability of the breaker A is so impaired, it Would be necessary to open the circuit breakers B and C connected to both sides of the breaker A in order to clear and isolate the fault. Thus, itwill be apparent that in order to provide the desired selectivity in operating the circuit breakers, it is important that the protective system be capable of distinguishing between faults internal to a circuit breaker and those external thereto and be capable of further distinguishing vbetween those external taults faults at the other side, ,Features of the protective equipment which provide this desired selectivity of operation will become a parent as the description proceeds. V

'For controlling tripping of the circuit breakers once the nature of the fault has been determined, differential relays 70 and 71 are provided. -Diiferenti-al relay 70 inestablish a tripping circuit for circuit breakers A and B. Similarly differential relay 71 includes normally-open contacts 73 which, when closed, establish a tripping circuit for circuit breakers A and C. To those skilled in the art it will be obvious that each of the circuit breakers controlled by a particular tripping circuit may have an electro-magnetically-controlled latchwhich is released to effect breaker opening in response to current flow through this particular tripping circuit. Accordingly, for the purposes of simplifying this description, these conventional details of the tripping circuits have been omitted.

Energization and operation of the relay 70 is effected from a differential protective circuit 80 including the current transformer secondary winding 60 of the breaker A and the current transformer secondary winding 81 of the breaker B. Each of these secondary windings 6t) and 81 is energized in accordance with the value of current fiowing in the portion of the primary conductor about which each secondary winding is disposed. As is well known in the art, the secondary windings are connected in such a manner that when these primary current values are vectorially equal, current merely circulates between the windings 6i) and 81 of the protective circuit 80, as a result of which the coil of relay 7 receives no effective current and remains decnergized. However, if these primary current values become unequal by a vector difference exceeding a predetermined amount, sufficient current will flow through the coil of relay 70 to operate the relay, thereby to close its contacts 7-2 and establish a trip circuit for breakers A and B. This equal primary current condition will exist so long as no fault is present in the Zone of the power circuit extending between windings 6t and 81. However, should a fault, such as at F, occur in the zone, the current flowing into the zone through one of the primary conductor portions would no longer be vectorially equal to the current flowing out of the zone through the other primary conductor portion. The resulting vector difference would produce a current flow in the differential protective circuit 80 which would be such as to operate the differential relay 7% so as to effect .tripping of breakers A and 13. Thus, the differential relay ill will operate in response to any fault occurring within the protected zone of the power circuit extending between the windings 60 and 81. Differential protective circuits of this general kind are well known, and may include either a direct connection between the current transformer windings, as is shown, or may alternatively include pilot wires or some other conventional signalling channel interconnecting windings.

Similarly, energization of the other differential relay 71 is effected from a differential protective circuit 82 including the current transformer windings 33 and 61. The winding of relay 71 is connected in its protective circuit in the same manner as described with respect to relay 7 0, so that should a fault occur in the protected zone of the power circuit extending between windings 83 and 61, such as at G, the relay 71 would operate to close and thereby trip breakers A and C.

To enable the relaying system to distinguish between a fault external to the circuit breaker A and one internal to this circuit breaker, a third current transformer winding 85 is provided. This third current transformer 85 'encicles both conductors, or arms, 50 and 51 of the current transformer primary winding. As shown in FIG. 1, this third winding 85 is disposed externally of the enclosure 22 in the region of the throat 4-3 of the tank 4-2 and is supported by suitable means 87 projecting outwardly from the throat 43. Preferably, this third wind ing 85 is wound about an annular magnetic core 86 encircling both the throat portion 43 of tank and the two arms 50 and 51 of the primary winding. The turns "of the winding 85 are insulated from each other and from the core 86 and the support 87 in a conventional manner. In certain portions of the present application, the core 86 is referred to as the magnetic circuit of the winding 85. c

The coil of a relay to is connected across the terminals of this winding so that the relay coil can be energized from the winding 85. When a net current exceeding a predetermined amount flows through the region encompassed by the magnetic circuit, or core, 86, sufficient current is induced in the current transformer winding 85 to effect operation of the relay 90. Operation of the relay closes a set of contacts 92 to complete a suitable trip circuit for the breakers A, B, and C.

So long as the primary circuit 50, 51, 52 of the current transformer assembly is sound, the winding 85 will not be effectively energized inasmuch as no net current is flowing in a path encompassed by its core 86. In this regard, any current entering the core region through one of the conductors, say 50, is effectively cancelled out by current leaving the core region through the other conductor 51. However, should the primary conductor 50, 51, 52 develop a fault to ground, say within the tank 42, the currents entering and leaving the region of the core 86 would no longer cancel out each other, and thus the winding 85 would be effectively energized. This would cause operation of the relay 90, which, in turn, would trip the circuit breakers A, B, and C, thus effectively isolating the fault in the desired manner. It will be apparent that for any fault to ground ocurring within the tank 4-2, irrespective of its particular location, the windings 85 will be energized to effect tripping of the breakers A, B, and C, as is desired.

In addition to being able to detect a fault occurring from the primary conductor 51, 52, 50, within the tank 42, the current transformer winding is able to detect any faults which might occur to ground from the conductors 50 and 51 within the porcelain column 40. Whether such faults followed a path to ground via the internal surface of the porcelain column it) or through the gaseous insulator directly to the throat 43 of the metallic tank 42, the path would still be disposed internally of the core of the third current transformer winding 85. As a result, there would be net cur-rent flowing internally of the current transformer winding 85 and such current would energize the winding 35 causing it to produce operation of the relay 9t} and resultant opening of the breakers A, B, and C, all as desired.

To insure that substantially all faults to ground occurring internally to the current transformer assembly follow a path disposed internally of the third current transformer winding 85, the tank 42 is connected to ground only at points beneath the current transformer winding 85. Thus, there is no significant likelihood of internal fault currents bypassing the third current transformer winding 85. Oonceivably the winding 85 could be bypassed by fault current resulting from a fault puncturing the porcelain column 40, but the possibility of such a puncture is so remote as to be essentially negligible.

It is unlikely that the internal circuit of the circuit breaker assembly will develop faults to ground at any location other than in the current transformer assembly. Thus, since our dis-closed arrangement is able to handle correctly all faults occurring internally of the current transformer assembly, as has been described hereinaibove, it is therefore capable of correctly handling substantially all ground faults which are likely to develop in the entire internal circuit of the circuit breaker assembly.

Faults occurring externally to the circuit breaker assembly, even those occurring in the immediate region Off the assembly, we prefer to treat as faults unlikely to impart the interrupting ability of the breaker. For example, a fault from either of the line terminals 58 or 59 to ground, are faults unlikely to impair the interrupting ability of the breaker, and such faults we prefer to isolate by opening only the breakers at the terminals of the faulted section. More specifically, a fault from the terminal 58 to ground, We prefer to isolate by opening only the breakers A and B, and a fault from terminal 59 to ground we prefer to isolate by opening only the breakers A and C.

7 7 To insure that such faults are relayed in this preferred manner, we provide'a shield, preferably in the form of a grading ring 93, which generally encompasses the current transformer winding 85 and is electrically interposed between the grounded components of the'assembly (including the winding 85) and substantially all of the high voltage parts of the assembly that are susceptible to external faults. only by conductive straps 94 disposed externally to the core, or magnetic circuit, of the current transformer Winding 85. As a result of this construction, external faults are prevented from following a breakdown path to ground disposed internally of the magnetic circuit of current transformer winding 85. Substantially all faults in the region of the current transformer winding 85 will be to the shield 93 rather than to the winding 85 or to the 'conductive parts 43, 45 disposed internally of the winding, and such faults will be directed to ground through the conductive straps 94 disposed externally to the current transformer Winding 85 and its core 86 thus effectively bypassing the winding 85 and the core 86. As a result, only the one differential relay in whose operating zone the external fault occurs operates in response to such fault. Since the interrupting ability of the breaker A is unimpaired by such external fault, it is capable of isolating the fault from the circuit at the other side of the breaker, thereby allowing uninterrupted service to be maintained over such circuit at the other side of the breaker.

Fault-s from the housing 23 to ground that are located external to the breaker, we also prefer to treat as external faults. Such faults will ordinarily be prevented from following a breakdown path to. ground internally of the core 86 of the current transformer secondary 85 and thus will be relayed as faults within the protective zone of differential circuit 80. This means that breakers A and B will open in response to such faults.

In the preceding two paragraphs and elsewhere in the presentapplication, reference is made to the breakdown path to ground followed by fault current. It is to be understood that this term is used to denote not only the arcing path followed by the fault current but also the path followed by the fault current through normally grounded conductive structure.

Some circuit breaker users might wish to relay external faults in the immediate vicinity of the breaker in the same manner as internal faults, on the assumption that such faults could possibly impair the interrupting ability of the breaker. Such circuit breaker users can be accommodated by utilizing an arrangement of the type shown in FIG. 4. The apparatus of FIG. 4 corresponds to that of FIG. 1 except for the fact that the shield 93 instead of being connected to ground only by structure disposed externally to the current transformer winding 85 is connected to ground only by structure disposed internally to this current transformer winding 85. In this latter regard, the shielding ring 93 is supported on the annular member 45 by conductive straps 95 located above the current transformer winding 85. No electrical connection between the tank 42 and the ring 93 is provided externally to the current transformer winding 85; As a result, any faults to the shielding ring 93 would be forced to follow 'a breakdown path to ground encompassed by the winding 85, i.e., via the straps 95 and thethroat 43 of tank 42.

From the above description of the performance: of the protective system, it will be apparent that although our' variety of different types of faults and initiating correct 7 operation of the circuit breakers in response to such.

faults. V

As pointed out hereinabove, our operating mechanism 32 generally'corresponds to that shown in the aforemen- This shield 93 is connected to ground tioned Beatty Patent 2,783,338. FIG. 2 provides a more detailed illustration of this operating mechanism. Referring now to FIG. 2, the movable contacts 28 and 30 are shown mounted on a casing 100 that is phyiscally supported on the housing 23 and is electrically connected thereto. A contact-supporting arm 1112 projects from the casing 101 to pivotally support the movable contacts 28 on a pivotlM. Another contact-supporting arm 106 projects from the opposite side of the casing 100 to pivotally support the movable contact 30 on a pivot 108. For preventing current from following a path between the movable contacts 28 and 30 that bypasses the primary winding 50, 52, 51, we construct the contact-supporting arm 106 in two parts that are electrically insulated from each other by means of a suitable insulating joint 10'].

The two movable contacts 28 and 30 are coupled to a cross head 110 that is vertically movable to effect simultaneous motion of the two contacts. The coupling between movable contact 28 and the cross head comprises a link 112 pivotally connected at its respective opposite ends to the contact 28 and the cross head 110. The coupling between the other movable contact 30 and the cross head 110 comprises a link 113 pivotally connected at its respective opposite ends to the contact 30 and the cross head. The link 113 is formed of insulating material in order to prevent current from following a path from the contact 30 to the cross head 110 that would bypass the primary winding 50, 52, 51. Motion of the cross head 110 in a downward direction causes the movable contacts 28 and 30 to move about their respective pivots 104 and 1% in a direction away from their respective stationary contacts 27 and 29. Motion of the cross head in an upward direction from its open position returns the contacts 28 and 30 to their closed positions shown. The mechanism for producing this vertical contact-controlling motion of the contacts 28 and 31 is disposed'within the casing 100'. Since this mechanism can be identical tothe mechanism of the aforementioned Beatty patent, ithas not been shown in the drawings.

As is pointed out in the Beatty patent, the circuit brealker also includes a blast valve 115 that is opened at about the instant of contact separation and is closed shortly after interruption is completed. Closing of the blast valve 115 after interruption can occur independently of contact-operation, so that the contacts can remain open while the blast valve is closed. The'blast valve 115 is operated in this manner by the mechanism within the casing 100 in the manner described in the Beatty patent, and reference may be had to that patent if more details are desired as to this matter. When the blast valve 115 opens, a blast of pressurized air flows from the interior of housing 23 to the surrounding atmosphere through a hollow exhaust casing 116 and then through an exhaust passage 118 opened by the blast valve 115. The approximate path of this blast of air is indicated by the arrows 120 of FIG. 2. At one side of the exhaust casing 116, this path extends from the interior of pressurized housing 23 through an orifice 124 provided in the hollow casing 116 and .then upwardly past the valve 115 into the exhaust passage 118. At the other side of the hollow exhaust casing 116, the blast of air flows through a similar orifice 126 upwardly through the hollow casing 116 past the blast valve 115 into the exhaust passage 1 18.

Thisblastof air serves to quickly extinguish the arcs drawn at the two sets of contacts 24 and 25 in the manner described in U.S. Patent 2,897,324 Schneider assigned to the assignee of the present invention. In extinguishing the are at the set of contacts 24-, the blast of air transfers one terminal of the are from the stationary contact 27 to an upstream probe or electrode 130 electrically connected to the stationary contact 27 and transfers the other terminal of the are from the movable contact 28 to a downstream probe or electrode 132 elecshort time after arrival of the arc in this position.

trically connected to the movable contact 28. The position of the are after such a transfer is indicated in dotted lines at 134. In this position, the arc is most vulnerable to extinction, and such extinction occurs within a The electrical connection between the downstream probe 132 and the movable contact 28 is through a conductive connection 140 shown in FIG. 3 and a connection 141 shown in FIG. 2. The connection 140 electrically interconnects the probe 132 to the casing 116 and this casing 116 is electrically connected to movable contact 28 through parts 141, 101}, and 102.

At the other side of the hollow casing 116 simultaneously with the above-described arc-extinction, the blast of air transfers the are at the set of contacts 25 to a position between an upstream probe or electrode 135 and a downstream probe or electrode 136. The are in its transferred position is indicated by dotted lines at 138. Thereafter the arc is quickly extinguished by the blast of air flowing through the orifice 126. The upstream probe 135 is electrically connected to the stationary contact 29 by a conductive support 139, and the downstream probe 136 is electrically connected to the movable contact 30 by means including conductor 144- shown in FIG. 2 and connections 145 shown in FIG. 3. It will be apparent from FIG. 3 that each of the probes is mounted on a semi-cylindrical shield that provides a surface along which the downstream arc terminal can run to reach the probe during the above-described transfer of the downstream terminal to the probe. These shields are respectively designated 132a and 136a.

To prevent a short circuit path from being present between the downstream terminals of the two arcs 134 and 138 when they are on their respective downstream probes 132 and 13 6, we locally insulate the probes 132 and 136 from each other. This forces current flowing between thetwo probes to follow a path through the primary winding 51, 52, 50 of the current transformer. The importance of this relationship will soon be described. With regard to this insulation, we form the hollow casing 116 in two separate parts locally insulated from each other. Referring to FIG. 3, one of these parts is designated 150. This part 150, which carries the orifice 126, is mechanically supported on the remainder of the hollow casing 116 by means of insulating connections 152. As shown in FIG. 2, the part 150 is also locally insulated from the interrupter housing 23 by means of insulation 155 and 156 at the bottom and top, respectively, of the part 156. The probe 136 is electrically connected to the part 151 through the previously-described shield 136a and connections 145, whereas the other probe 132 is electrically connected to the remainder of hollow casing 116 through the previously-described shield 132a and connections 140. Thus, current through the are 138, rather than flowing directly between the probes 132. and 136, follows a path through the primary conductor 50, 52, 51 of the current transformer. This path through the current transformer extends from probe 136 through connections 136a, 145, the part 150, flexible connection 144, the movable contact 3i), connection 55, the primary winding 51), 52, 51, and the parts 54, 2%, 102, 1%, 141 to the other probe 132.

If current were permitted to flow directly between the probes instead of being forced to flow through the primary winding of the current transformer, then the two secondary windings '60 and 61 would receive no current during .the interrupting period. If the interrupting period were relatively long, then both differential circuits 80 and 82 would operate. This could be an erroneous operation if the fault that initiated breaker operation was in the protective zone of only one of these differential circuits. By forcing current between the probes to flow through the primary of the current transformer during interruption, we can avoid such erroneous operation.

In certain circuit breakers built in the general manner illustrated, the arcs 134 and 138 can be extinguished so rapidly that the differential protective circuits and 82 would not have time to operate in response to the above-described by-passing of the current transformer primary winding. In other words, the arcs would be consistently extinguished in less time than the affected differential circuit could cause its relay to operate. This would prevent false operation of the relay. Accordingly, in such breakers, it is permissible to electrically connect the probes 132 and 136 directly together so that current can flow between the probes during arcing by a path that bypasses the primary winding 51, 52, 50 of the current transformer. It is sufiicient merely to insulate the movable contact 30 from the remainder of the hollow casing 116 without providing insulation between the probes. The insulation between the movable contact 30 and the hollow casing 116 would force current to flow through the current transformer during normal closed circuit conditions, but during the short interrupting period, current would be allowed to flow directly between the probes. The high speed of arc extinction would prevent current ilow over this path from causing false operation of either differential circuit.

Although insulation between the probes 132 and 136 is not ordinarily required for such high speed breakers, as is explained above, we still prefer to include such insulation in order to insure against the above-described false operation by forcing the current to flow between the probes 132, 136 through the primary conductor 51, 52, 59 even during interruption.

While we have shown and described particular embodiments of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention in its broader aspects and We, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

=What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit breaker assembly comprising a metallic housing at high potential, two sets of separable contacts disposed within said housing, means for separating the contacts of both of said sets to effect circuit interruption Within said housing, an enclosure comprising a hollow insulating column and a tank disposed adjacent one end of said column, means for supporting said housing on the other end of said column so that said column insulates said housing from ground, a current transformer primary winding located electrically between said two sets of contacts, insulation for forcing current flowing between said two sets of contacts to follow a path through said primary winding, said primary winding comprising a pair of series-connected arms forming a loop, one of said arms extending from one set of contacts through said insulating column into said tank and the other of said arms extending from said tank back through said insulating column to the other set of contacts, a first current transformer secondary winding located in said tank and inductively coupled to said primary winding, a second current transformer secondary winding having -a magnetic circuit disposed externally to said enclosure and about both of said arms so that said second winding is normally deenergized, means for forcing substantially all faults occurring within said enclosure to follow a path to ground so located that said fault produces a net flow of current through the region disposed internally of the magnetic circuit of said second secondary winding, and means for forcing substantially all faults external to said circuit breaker in the region of said insulating column consistently to follow a breakdown path to ground which has a predetermined electrical location relative to the magnetic circuit of said second winding.

2. The circuit breaker of claim 1 in combination with a pair of spaced-apart high voltage bushings projecting into saidrnetal housing for carrying current to and from said contacts, said bushings extending transversely of said insulating column, and means for supporting one contact of each of said sets on one of said bushings.

3. In the circuit breaker of claim 1, a pair of electrodes,

means for electrically connecting one of the electrodes directly to said metallic housing, means for insulating the other of said electrodes from said housing except for a connection provided through the primary Winding of said current transformer, means for transferring one terminal of an are drawn at one of said sets of contacts to said first electrode, and means for transferring one terminal of an arc drawn at the other set of contacts to said second electrode.

4. In the circuit breaker of claim 1, a pair of electrodes, means for transferring one terminal of an are drawn at one set of contacts mom of said electrodes, means for transferring one terminal of an are drawn at the other set. of contacts to the other of said electrodes, and insulating means for forcing current flowing between said two arcs through said electrodes to follow a path extending through the primary winding of said current transformer.

5. An electric circuit breaker comprising a metallic housing at high potential, two sets of separable contacts .disposed within said housing, means for separating the contacts of both of said sets to effect circuit interruption within said housing, a hollow insulating column having one end adjacent said housing and the other end adjacent vground for supporting said housing and insulating said set of'said contacts through said insulating column and then back through said column to the other set of said contacts, a secondary winding inductively coupled to said primary winding and located at said other end of said insulating column. i

6. The circuit breaker of claim 5 in combination with a pair of spaced-apart high voltage bushings projecting into said metal housing for carrying current to and from said contacts, said bushings extending transversely of said insulating column, and means for supporting one contact of each of said sets on one of said bushings.

' 7. In the circuit breaker of claim 5, a pair of electrodes, means for transferring one terminal of an arc drawn at one set of contacts to one'of said electrodes,

'means for transferring one terminal of an are drawn at the other set of contacts to the other of said electrodes,

and insulating means for forcing current flowing between .said two arcs through said electrodes to follow a path extending through the primary winding of said current transformer.

References (Iited in the file of this patent UNITED STATES PATENTS Coggeshall et al. Aug. 27, 1957 Wilson f Apr. 5,'l 960 

1. AN ELECTRIC CIRCUIT BREAKER ASSEMBLY COMPRISING A METALLIC HOUSING AT HIGH POTENTIAL, TWO SETS OF SEPARABLE CONTACTS DISPOSED WITHIN SAID HOUSING, MEANS FOR SEPARATING THE CONTACTS OF BOTH OF SAID SETS TO EFFECT CIRCUIT INTERRUPTION WITHIN SAID HOUSING, AN ENCLOSURE COMPRISING A HOLLOW INSULATING COLUMN AND A TANK DISPOSED ADJACENT ONE END OF SAID COLUMN, MEANS FOR SUPPORTING SAID HOUSING ON THE OTHER END OF SAID COLUMN SO THAT SAID COLUMN INSULATES SAID HOUSING FROM GROUND, A CURRENT TRANSFORMER PRIMARY WINDING LOCATED ELECTRICALLY BETWEEN SAID TWO SETS OF CONTACTS, INSULATION FOR FORCING CURRENT FLOWING BETWEEN SAID TWO SETS OF CONTACTS TO FOLLOW A PATH THROUGH SAID PRIMARY WINDING, SAID PRIMARY WINDING COMPRISING A PAIR OF SERIES-CONNECTED ARMS FORMING A LOOP, ONE OF SAID ARMS EXTENDING FROM ONE SET OF CONTACTS THROUGH SAID INSULATING COLUMN INTO SAID TANK AND THE OTHER OF SAID ARMS EXTENDING FROM SAID TANK BACK THROUGH SAID INSULATING COLUMN TO THE OTHER SET OF CONTACTS, A FIRST CURRENT TRANSFORMER SECONDARY WINDING LOCATED IN SAID TANK AND INDUCTIVELY COUPLED TO SAID PRIMARY WINDING, A SECOND CURRENT TRANSFORMER SECONDARY WINDING HAVING A MAGNETIC CIRCUIT DISPOSED EXTERNALLY TO SAID ENCLOSURE AND ABOUT BOTH OF SAID ARMS SO THAT SAID SECOND WINDING IS NORMALLY DEENERGIZED, MEANS FOR FORCING SUBSTANTIALLY ALL FAULTS OCCURRING WITHIN SAID ENCLOSURE TO FOLLOW A PATH TO GROUND SO LOCATED THAT SAID FAULT PRO- 